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Method and apparatus for retrieving a hovering aircraft
US8708278B2
United States
- Inventor
Brian T. McGeer Andreas H. von Flotow Corydon C. Roeseler - Current Assignee
- Aerovel Corp
Worldwide applications
Application US13/900,191 events
2013-05-22
2013-05-22
2014-03-20
2014-04-29
Application granted
2014-04-29
Status
Active
2029-10-08
Adjusted expiration
Description
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This application is a continuation of, and claims priority to and the benefit of, U.S. patent application Ser. No. 13/717,147, filed on Dec. 17, 2012, which is a continuation of, and claims priority to and the benefit of, U.S. patent application Ser. No. 13/540,032, filed on Jul. 2, 2012, which issued as U.S. Pat. No. 8,348,193 on Jan. 8, 2013, which is a continuation of, and claims priority to and the benefit of, U.S. patent application Ser. No. 13/024,843, filed on Feb. 10, 2011, which issued as U.S. Pat. No. 8,245,968 on Aug. 21, 2012, which is a divisional of, and claims priority to and the benefit of, U.S. patent application Ser. No. 11/837,878, filed on Aug. 13, 2007, which issued as U.S. Pat. No. 7,954,758 on Jun. 7, 2011, which claims priority to and the benefit of U.S. Provisional Patent Application No. 60/823,442, filed on Aug. 24, 2006, now expired, the entire contents of each of which are incorporated herein by reference.
The present application relates to the following commonly-owned co-pending patent applications: U.S. patent application Ser. No. 13/717,147, filed on Dec. 17, 2012; U.S. patent application Ser. No. 13/527,177, filed on Jun. 19, 2012; U.S. patent application Ser. No. 13/743,069, filed on Jan. 16, 2013; U.S. patent application Ser. No. 13/899,172, filed on May 21, 2013; U.S. patent application Ser. No. 13/901,283, filed on May 23, 2013; U.S. patent application Ser. No. 13/901,295, filed on May 23, 2013; and U.S. patent application Ser. No. 14/034,097, filed on Sep. 23, 2013.
This invention was made with U.S. Government support under Contract No. W31P4Q-06-C-0043, effective Nov. 23, 2005 (“the contract”), issued by U.S. Army Aviation and Missile Command. The U.S. Government has certain rights in the invention. More specifically, the U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of the contract.
1. Field
The present disclosure addresses retrieval of a hovering aircraft, especially in turbulent winds or onto a rough or irregularly-moving surface, such as the deck of a ship in a rough sea. The present disclosure is especially suited to unmanned aircraft of small size, and requires only modest accuracy in automatic or manual piloting.
2. Description of Prior Art
Hovering aircraft, be they helicopters, thrust-vectoring jets, “tail-sitters,” or other types, usually land by gently descending in free thrust-borne flight onto a landing surface, coming to rest on an undercarriage of wheels, skids, or legs. This elementary technique can be problematic in certain situations, for example when targeting a small, windswept landing pad on a ship moving in a rough sea. Decades ago, the Beartrap or RAST system was developed to permit retrieval with acceptable safety in such conditions. Retrieval with this system involves securing a line between a helicopter and landing deck, and then winching the helicopter down onto a trolley. The helicopter is fastened to the trolley. After retrieval, the trolley is used to move the helicopter along the deck. The system is effective and widely used, but requires an expensive and substantial plant in the landing area, and coordination between aircraft and ground crew. Furthermore, the helicopter must carry a complete undercarriage in addition to the necessary Beartrap components.
By comparison, simple methods for retrieving aircraft from wing-borne flight into a small space have been described in U.S. Pat. No. 6,264,140 and U.S. Pat. No. 6,874,729. These involve flying the aircraft into a cable suspended in an essentially vertical orientation. Typically, the cable strikes a wing of the aircraft and slides spanwise along the wing into a hook; the hook snags the cable; the cable decelerates the aircraft briskly but smoothly; and the aircraft comes to rest hanging by its hook. Advantages of this technique include: simplicity of the apparatus; relatively easy targeting, since the aircraft can make contact anywhere within its wingspan and almost anywhere along the cable; elimination of undercarriage from the aircraft; and safety, since the aircraft simply continues in wing-borne flight if it misses the cable, and since all components, apart from the cable itself, are kept well clear of the flight path.
One embodiment of the present disclosure provides for snag-cable retrieval of thrust-borne or hovering aircraft, and particularly those with large rotors. The present disclosure offers the same advantages as does snag-cable retrieval for wing-borne aircraft; namely, simplicity, relatively easy targeting, elimination of undercarriage, and safety.
Furthermore, since loads can be low during retrieval from hover, the apparatus can be light, inexpensive, and easy to deploy. Easy targeting makes the technique well-suited for both manual control and economical automation.
Additional features and advantages are described herein, and will be apparent from the following Detailed Description and the Figures.
If the approach speed of the helicopter 1 is sufficiently high, then the cable 12 may have to comply in order to make deceleration loads acceptably small. This may be done by: (a) incorporating elastic segments into the cable 12; or (b) by paying-out slack from a winch 18 in order to control tension in the cable 12; or (c) by a combination thereof. In either case, provision may be made quickly to take up the slack during the latter part of deceleration in order to limit sag of the helicopter 1 as it comes to rest.
It should be noted that instead of deploying the retrieval-fixture interceptor downward as in FIG. 1 , the helicopter 1 in an alternative embodiment could deploy the interceptor upward from its rotor hub 3. It would then approach so that its rotor 2 passes below rather than above the cable 12, and it would come to rest hanging right-side-up rather than upside-down. While coming to rest right-side-up would be desirable, especially for a manned helicopter, passing above the cable 12 as in FIG. 1 offers two safety advantages over passing below. First, it increases the clearance between the cable 12 and the rotor 2 during approach. Second, it permits the helicopter 1 to attempt a climb to test for capture (much as a fixed-wing aircraft landing on an aircraft carrier increases power immediately at touchdown). Thus, shortly after passing the cable axis 14, or upon detecting an indication of contact with or capture of the cable 12, power to the rotor 2 can be increased. If capture has not occurred, then the helicopter 1 will climb away from the retrieval area and can return for another approach. If the helicopter 1 fails to climb, then this can be taken as confirmation that capture has occurred, and power can be reduced. The helicopter 1 will then descend, and be left hanging upside-down from the cable 12. Swinging motion, including rotations about the approach axis 42 caused by rotor gyroscopic effect, can be damped by appropriate management of rotor thrust and in-plane moments during deceleration.
In any of these example embodiments, should the cable 12 not be captured because of incorrect altitude, failure to capture can be recognized as the cable axis 14 is passed. The aircraft can then climb away from the retrieval area and return for another approach.
For successful capture, the aircraft 28 must contact the cable 12 in an aperture between the wing 29 and the hook 9. When the airspeed vector VA is into-wind VW, the thrust-vector tilt θ makes the aperture on the downwind side of the aircraft hd broader than the aperture on the upwind side hu. Hence, guidance for a horizontal approach can be less precise if the aircraft approaches the cable 12 while moving downwind rather than upwind. In a sufficiently strong wind, tilt of the thrust vector could be so large that the upwind aperture hu would vanish, and a horizontal approach would have to be made downwind in order to engage the cable 12.
The approach, however, need not be horizontal. FIG. 8 shows an alternative in which the aircraft 28 approaches while descending into-wind with knife-edge wing orientation. If the slope γ of the approach path is selected to be approximately equal to the thrust-vector tilt θ, then the aperture hu for successful capture of the cable 12 is kept large. For a given wind speed VW, this form of upwind approach requires more thrust (but not necessarily more power) than a downwind approach since it calls for higher airspeed.
A further possibility, as shown in FIG. 9 , is to approach with the wing 29 in a lifting rather than knife-edge orientation. In this case, the vector sum of thrust T and lift L balances drag D and weight W. Again, the aircraft 28 presents maximum capture aperture hu to the cable 12 by approaching into-wind while descending on a slope γ which is approximately equal to the thrust-vector tilt θ. If the wind speed exceeds the stall airspeed in wing-borne flight, then descent can be vertical.
Of these approach methods, downwind drift in knife-edge orientation as in FIG. 7 requires the least thrust in a light wind. Wing-borne upwind descent as in FIG. 9 requires the least thrust in a strong wind. Hence, the best choice of approach path and aircraft orientation will depend at least in part on wind speed.
In an automatic approach, thrust-vector tilt θ and rotor power are adjusted to regulate the approach velocity vector VG. Upon encountering the cable 12, progress is retarded, and the automatic-control logic calls for the thrust vector T to be tilted toward the approach path 42. This causes the aircraft 28 to rotate around the cable 12 in the desired direction indicated by arrow 19 in FIG. 4B , so that sliding of the cable 12 into the hook 10 is promoted.
In the embodiment of FIGS. 12A , 12B, 12C, and 12D, the cantilever boom 48 is rotatable on a hinge 50 about a vertical axis 49 as shown by arrow 58. An aerodynamic surface 52 orients the boom 48 passively relative to the wind. Similarly, the boom 48 is rotatable about a horizontal axis 14, and is rigidly connected to an aerodynamic surface 53. The weight of this surface 53, and its attachment 57 to the boom 48, are chosen so that the latches 56 are oriented appropriately for a horizontal approach in calm wind. The area of the surface 53 is chosen so that as the wind speed increases, the latches orient appropriately for a descending approach as shown in FIG. 8 and FIG. 9 .
In the embodiments illustrated above, the aircraft's thrust axis rotates substantially out of the vertical during the course of retrieval. FIGS. 13A , 13B, 13C, and 13D show an alternative embodiment in which the thrust axis remains near vertical until the aircraft “parks.” The aircraft approaches and captures a retrieval cable 12 as in FIGS. 4A and 4B . Then, upon detecting contact, it applies pitch and yaw torques, for example by appropriate adjustment of rotor cyclic pitch, so that rotation about the cable is arrested and near-vertical orientation is maintained. By further application of control torques, the aircraft slides along the cable such that it is guided by the cable into a docking fixture 5 a near a cable support as shown in FIGS. 13B and 13C . The docking fixture may include devices suitable for orienting and securing the aircraft in a desired position, which is provided so that secure docking can be detected, after which the aircraft's motor can be shut down. In one example, the docking fixture includes an arm, such as the arm illustrated in FIGS. 13A , 13B, 13C, and 13D, configured to engage and secure the aircraft. The docking station may further include suitable devices for conveniently servicing the aircraft, stowing the aircraft, or launching the aircraft for another flight as shown in FIG. 13D .
It should be understood that various changes and modifications to our illustrative embodiments will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.
Claims (28)
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Claims (28)
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1. A method for capturing a flying object, said method comprising:
(a) causing a member connected to a body of the flying object to contact a fixture by motion of the flying object relative to the fixture;
(b) thereafter, translating the flying object relative to the fixture toward a docking fixture;
(c) receiving the flying object in the docking fixture; and
(d) engaging a portion of the flying object with an arm of the docking fixture.
2. The method of claim 1 , wherein causing the member to contact the fixture includes causing the member to contact the fixture such that the member removably attaches to the fixture.
3. The method of claim 1 , which includes stowing the flying object after the docking fixture receives the flying object.
4. The method of claim 1 , which includes servicing the flying object after the docking fixture receives the flying object.
5. The method of claim 4 , wherein said servicing is performed automatically.
6. The method of claim 1 , which includes facilitating launch of the flying object after the docking fixture receives the flying object.
7. The method of claim 1 , which includes holding said portion of the flying object with the arm.
8. The method of claim 1 , which includes guiding the flying object into a desired resting position as the flying object translates relative to the fixture toward the docking fixture.
9. The method of claim 8 , which includes detecting that the flying object has been guided into said desired resting position.
10. The method of claim 1 , which includes orienting the flying object after the docking fixture receives the flying object.
11. A method for capturing a flying object, said method comprising:
(a) after a member connected to a body of the flying object contacts and removably attaches to a fixture, translating the flying object relative to the fixture toward a docking fixture;
(b) receiving the flying object in the docking fixture; and
(c) engaging a portion of the flying object with an arm of the docking fixture.
12. The method of claim 11 , which includes stowing the flying object after the docking fixture receives the flying object.
13. The method of claim 11 , which includes servicing the flying object after the docking fixture receives the flying object.
14. The method of claim 13 , wherein said servicing is performed automatically.
15. The method of claim 11 , which includes facilitating launch of the flying object after the docking fixture receives the flying object.
16. The method of claim 11 , which includes holding said portion of the flying object with the arm.
17. The method of claim 11 , which includes guiding the flying object into a desired resting position as the flying object translates relative to the fixture toward the docking fixture.
18. The method of claim 17 , which includes detecting that the flying object has been guided into said desired resting position.
19. The method of claim 11 , which includes orienting the flying object after the docking fixture receives the flying object.
20. A method for capturing a flying object, said method comprising:
(a) receiving the flying object in a docking fixture after:
(i) a member connected to a body of the flying object contacts a fixture by motion of the flying object relative to the fixture;
(ii) the member removably attaches to the fixture; and
(iii) the flying object is translated relative to the fixture toward the docking fixture; and
(b) engaging said portion of the flying object with an arm of the docking fixture.
21. The method of claim 20 , which includes stowing the flying object after the docking fixture receives the flying object.
22. The method of claim 20 , which includes servicing the flying object after the docking fixture receives the flying object.
23. The method of claim 22 , wherein said servicing is performed automatically.
24. The method of claim 20 , which includes facilitating launch of the flying object after the docking fixture receives the flying object.
25. The method of claim 20 , which includes holding said portion of the flying object with the arm.
26. The method of claim 20 , which includes guiding the flying object into a desired resting position as the flying object translates relative to the fixture toward the docking fixture.
27. The method of claim 26 , which includes detecting that the flying object has been guided into said desired resting position.
28. The method of claim 20 , which includes orienting the flying object after the docking fixture receives the flying object.